<jer### [at] atosorigincom>  wrote:

> The 'sturm' keyword is such a case (probably the only one), where the default
> choosen was speed against accuracy (it apply to sor, some lathe, blob, cubic,
> poly, some prism and quartic).

Actually, this is not the case.  Any platform and library could provide a
square root that provides the same precision as the you get with "sturm" *.
It is just that on most platforms this is not done by default and POV-Ray
contains code that works around this compiler/library/platform limitation.
Kind of a platform specific hack you can add to your scenes, just that it is
necessary on all current desktop platforms.

I would also expect the precision of the default square root to be good
enough on platforms that support 128 bit floating-point arithmetic.  Then
"sturm" would not be needed at all.


    Thorsten


* Yes, we are talking about polynoms here, but internally POV-Ray uses
"sqrt" to find the roots, while "sturm" switches to the sturmian sequence to
solve it.  Effectively, the limited precision of "sqrt" is one of the
problems together with the use of some other library functions such as "cos"
and "acos" which are frequently based on approximations in C libraries...


____________________________________________________
Thorsten Froehlich, Duisburg, Germany
e-mail: tho### [at] trfde

Visit POV-Ray on the web: http://mac.povray.org

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